From af338a34c04d4e7fb741698521e9beb2f53027e1 Mon Sep 17 00:00:00 2001
From: Itamar <itamar8910@gmail.com>
Date: Wed, 15 Apr 2020 21:03:22 +0300
Subject: [PATCH] LibDebug: Add ContinueBreakAtSyscall decision

When the user of the DebugSession uses this decision, the debugged
program will be continued until it is either stopped by a singal (e.g
as a reuslt of a breakpoint), or enters a syscall.
---
 Libraries/LibDebug/DebugSession.cpp | 16 ++++++-
 Libraries/LibDebug/DebugSession.h   | 65 +++++++++++++++++++----------
 2 files changed, 58 insertions(+), 23 deletions(-)

diff --git a/Libraries/LibDebug/DebugSession.cpp b/Libraries/LibDebug/DebugSession.cpp
index 5519c73289..65261dfe19 100644
--- a/Libraries/LibDebug/DebugSession.cpp
+++ b/Libraries/LibDebug/DebugSession.cpp
@@ -184,14 +184,26 @@ void DebugSession::set_registers(const PtraceRegisters& regs)
     }
 }
 
-void DebugSession::continue_debugee()
+void DebugSession::continue_debugee(ContinueType type)
 {
-    if (ptrace(PT_CONTINUE, m_debugee_pid, 0, 0) < 0) {
+    int command = (type == ContinueType::FreeRun) ? PT_CONTINUE : PT_SYSCALL;
+    if (ptrace(command, m_debugee_pid, 0, 0) < 0) {
         perror("continue");
         ASSERT_NOT_REACHED();
     }
 }
 
+int DebugSession::continue_debugee_and_wait(ContinueType type)
+{
+    continue_debugee(type);
+    int wstatus = 0;
+    if (waitpid(m_debugee_pid, &wstatus, WSTOPPED | WEXITED) != m_debugee_pid) {
+        perror("waitpid");
+        ASSERT_NOT_REACHED();
+    }
+    return wstatus;
+}
+
 void* DebugSession::single_step()
 {
     auto regs = get_registers();
diff --git a/Libraries/LibDebug/DebugSession.h b/Libraries/LibDebug/DebugSession.h
index e3138c1dcb..e52679640e 100644
--- a/Libraries/LibDebug/DebugSession.h
+++ b/Libraries/LibDebug/DebugSession.h
@@ -71,7 +71,15 @@ public:
     PtraceRegisters get_registers() const;
     void set_registers(const PtraceRegisters&);
 
-    void continue_debugee();
+    enum class ContinueType {
+        FreeRun,
+        Syscall,
+    };
+    void continue_debugee(ContinueType type = ContinueType::FreeRun);
+
+    //returns the wstatus result of waitpid()
+    int continue_debugee_and_wait(ContinueType type = ContinueType::FreeRun);
+
     void* single_step();
 
     template<typename Callback>
@@ -83,12 +91,14 @@ public:
     enum DebugDecision {
         Continue,
         SingleStep,
+        ContinueBreakAtSyscall,
         Detach,
         Kill,
     };
 
     enum DebugBreakReason {
         Breakpoint,
+        Syscall,
         Exited,
     };
 
@@ -112,36 +122,39 @@ void DebugSession::run(Callback callback)
 
     enum class State {
         FreeRun,
+        Syscall,
         ConsecutiveBreakpoint,
         SingleStep,
     };
 
     State state { State::FreeRun };
 
+    auto do_continue_and_wait = [&]() {
+        int wstatus = continue_debugee_and_wait((state == State::FreeRun) ? ContinueType::FreeRun : ContinueType::Syscall);
+
+        // FIXME: This check actually only checks whether the debugee
+        // stopped because it hit a breakpoint/syscall/is in single stepping mode or not
+        if (WSTOPSIG(wstatus) != SIGTRAP) {
+            callback(DebugBreakReason::Exited, Optional<PtraceRegisters>());
+            m_is_debugee_dead = true;
+            return true;
+        }
+        return false;
+    };
+
     for (;;) {
-        if (state == State::FreeRun) {
-            continue_debugee();
-
-            int wstatus = 0;
-            if (waitpid(m_debugee_pid, &wstatus, WSTOPPED | WEXITED) != m_debugee_pid) {
-                perror("waitpid");
-                ASSERT_NOT_REACHED();
-            }
-
-            // FIXME: This check actually only checks whether the debugee
-            // stopped because it hit a breakpoint/is in single stepping mode or not
-            if (WSTOPSIG(wstatus) != SIGTRAP) {
-                callback(DebugBreakReason::Exited, Optional<PtraceRegisters>());
-                m_is_debugee_dead = true;
+        if (state == State::FreeRun || state == State::Syscall) {
+            if (do_continue_and_wait())
                 break;
-            }
         }
 
         auto regs = get_registers();
         Optional<BreakPoint> current_breakpoint;
 
-        if (state == State::FreeRun) {
+        if (state == State::FreeRun || state == State::Syscall) {
             current_breakpoint = m_breakpoints.get((void*)((u32)regs.eip - 1));
+            if (current_breakpoint.has_value())
+                state = State::FreeRun;
         } else {
             current_breakpoint = m_breakpoints.get((void*)regs.eip);
         }
@@ -153,10 +166,19 @@ void DebugSession::run(Callback callback)
             disable_breakpoint(current_breakpoint.value());
         }
 
-        DebugDecision decision = callback(DebugBreakReason::Breakpoint, regs);
+        DebugBreakReason reason = (state == State::Syscall && !current_breakpoint.has_value()) ? DebugBreakReason::Syscall : DebugBreakReason::Breakpoint;
+        DebugDecision decision = callback(reason, regs);
+
+        if (reason == DebugBreakReason::Syscall) {
+            // skip the exit from the syscall
+            if (do_continue_and_wait())
+                break;
+        }
 
         if (decision == DebugDecision::Continue) {
             state = State::FreeRun;
+        } else if (decision == DebugDecision::ContinueBreakAtSyscall) {
+            state = State::Syscall;
         }
 
         if (current_breakpoint.has_value()) {
@@ -174,9 +196,10 @@ void DebugSession::run(Callback callback)
 
         if (decision == DebugDecision::SingleStep) {
             state = State::SingleStep;
-        } else {
-            // TODO: implement DebugDecision:: Kill, Detach
-            ASSERT(decision == DebugDecision::Continue);
+        }
+
+        if (decision == DebugDecision::Kill || decision == DebugDecision::Detach) {
+            ASSERT_NOT_REACHED(); // TODO: implement
         }
 
         if (state == State::SingleStep) {